OOP questions

Question 1

Advantages of OOP

Answer 1

• Can modify and maintain existing code more easily.
• Reuse of code in other programs through libraries
• Clear modular structure with a defined interface -> can abstract and hide away details.

Question 2

Advantages of Constants

Answer 2

• They have meaningful identifiers which make code easier to follow and maintain
• Constants only have to be updated in one place if the value changes.

Question 3

“Inherits” meaning

Answer 3

The child class gains all of the non-private methods of the parent and all of the attributes of the parent.

Question 4

What is Aggregation Association?

Answer 4

• Weaker association
• The child class cannot exist independently of the parent class
• Real-life example: A person in a car

Question 5

What is Composition association?

Answer 5

• Stronger association
• The child class cannot exist independently of the parent class.
• Real-life example: A wheel of a car

Question 6

What is encapsulation?

Answer 6

• Used to hide data and methods, which prevents them from being accessed and changed.
• Distinguishes attributes/methods as public, protected and private.

Question 7

What is a public method / attribute ?

Answer 7

A method/attribute accessible from outside the class.

Question 8

What is a private method/attribute?

Answer 8

Private methods/attribute are accessible in their own class

Question 9

How can you access private attributes?

Answer 9

Using a defined method, e.g. GetSymbol()

Question 10

What are protected methods / attributes?

Answer 10

Only current class can access methods / attributes.

Question 11

What programming language doesn’t recognise protected attributes / methods?

Answer 11

Python!

Question 11

How can you update private attributes?

Answer 11

Using a setter method.

E.g. ChangeSymbolInCell()

Question 11

What is Overriding?

Answer 11

When a method in a child class overrides a method or attribute in a parent class.

Question 12

What is Polymorphism?

Answer 12

Allows us to have a function that can take on many forms of its parameters by using overriding.

E.g. the built in function len ()

Question 13

What is a static attribute?

Answer 13

Static attributes are defined for the class and can be accessed without creating an object instance.

Question 14

What is an abstract method?

Answer 14

The method isn’t supplied in the base class, which forces the method to be implemented in the subclass (child class)

Question 15

What is a static method?

Answer 15

A method that doesn’t need to be accessed through object instantation.

Question 16

What is a virtual method?

Answer 16

A method defined in a superclass that can be overridden by methods in a subclass.

Question 17

What is the difference between an abstract and virtual method?

Answer 17

Virtual methods have implementation, whereas abstract methods do not.

Question 18

What is special about every method in Python?

Answer 18

All methods in Python are virtual.

Question 19

What is an interface?

Answer 19

A class containing abstract methods. It enforces classes to have a fixed set of methods, with the methods being run from the class and not the interface.

Question 20

How do you indicate inheritance in a UML class diagram?

Answer 20

Have the child class pointing to the parent class using an arrow with its head shaded in.

Question 21

How do you indicate composition in a UML class diagram?

Answer 21

Using an arrow with its head as a shaded in black diamond.

Question 22

How do you indicate aggregation in a UML class diagram?

Answer 22

Using an arrow with its head as a white diamond.

Question 23

How do you indicate that an attribute / method in a UML class diagram is public?

Answer 23

Use a plus sign ( + )

Question 24

How do you indicate that an attribute / method in a UML class diagram is protected?

Answer 24

Use a hashtag ( # )

Question 25

How do you indicate that an attribute / method in a UML class diagram is private?

Answer 25

Use a minus sign ( - )

Question 26

What are the benefits of composition over inheritance?

Answer 26

• Each class can be tested more easily using composition. It isn’t possible to test a child class independently from a parent class using inheritance.
• There can be side effects for child classes if a method in the parent class is changed.

Question 27

What is the benefit of using encapsulation?

Answer 27

Allows programmers to make future changes to the code more easily, as making private attributes and methods protects other parts of the code from change.

Question 28

What is the benefit of using interfaces instead of implementation?

Answer 28

Allows programmers to have a framework for all of the classes, as it allows a way to find commonality between unrelated classes that need common methods.